An optical system of a sensor head of a conventional optical displacement sensor is shown in FIG. 28. In the drawing, numeral 500 denotes a sensor head unit, numeral 501 denotes a laser diode for emitting a sectional light for the light sectional method, numeral 502 denotes a slit for making the cross section of the sectional light into a linear shape, numeral 503 denotes a light emitting lens, numeral 504 denotes a light receiving lens, numeral 505 denotes a light receiving device such as a PDS, one-dimensional CCD or the like, numeral 600 denotes a measurement object, numeral 700 denotes a stage, and SP denotes a sectional light image (linear bright line) formed on a measurement position of the measurement object 600.
Because the light receiving device 505 of the conventional optical displacement sensor consisted of a PSD or one-dimensional CCD that can capture only one-dimensional information, a highly complicated scanning mechanism was necessary to effect a relative movement between the sensor head 500 and the measurement object 600 as shown in FIG. 29, and a problem has been pointed out that this leads to an increase in the cost.
An optical displacement sensor using a two dimensional imaging device as a light receiving device has recently been proposed, and the two dimensional imaging device used in such a displacement sensor typically consisted of a low-end two dimensional CCD which is typically used in digital cameras and video cameras to minimize cost.
When a two dimensional CCD is used as a light receiving device of a displacement sensor, it is required to have a large number (such as hundreds) of pixels to achieve a required precision or resolution in the direction of displacement measurement, but a relatively small number (tens to one hundred) of pixels in the direction perpendicular to the measurement direction.
However, the pixel arrangement of such a low end two dimensional CCD includes hundreds to thousands (with an aspect ratio of 3 to 4) in both the vertical and horizontal directions as shown in FIG. 30. Therefore, a significant time period is required to read the received electric charges for each shot, and this impairs the responsiveness of the measurement. Also, OB denotes optically black region.
As a measure for achieving high speed shots, it is possible to use a specialized CCD imaging device having a smaller number of horizontal lines (60 to 70 lines for instance) so as to suit the elongated rectangular field of view for measurement. However, such a CCD imaging device must be specially ordered, and tends to be expensive because of the high cost of development and the long time period required for the development.
This invention was made in view of such problems, and its primary object is to provide a displacement sensor which is suited for imaging an elongated field of view at high speed and at high precision for a variety of process modes of measurement in a highly responsive manner, and at the same time, can be provided at low manufacturing cost.